Ablation of ATJ Graphite at High Temperatures

Lundell, J. H.; Dickey, R. R.

doi:10.2514/3.50451

Cited by 56 publications

(10 citation statements)

References 9 publications

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“…A s = surface area, mm 2 D = module diameter, mm H t = total enthalpy, MJ/kg m = mass loss, g P a -stagnation pressure behind the shock, atm #o i = stagnation heat flux for 0.3048-m-radius sphere, W/cm 2 s = module surface recession, mm T w = wall temperature, K t = minimum aeroshell thickness, mm X -vertical position with respect to nozzle center, mm Y = horizontal position with respect to nozzle center, mm p = ablating material density, g/cm 3 Subscripts av = average ref = reference t = Total w = wall…”

Section: Nomenclaturementioning

confidence: 99%

Ablation response testing of simulated radioisotope power supplies

Lutz

Chan

1994

Journal of Spacecraft and Rockets

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Results of an experimental program to assess the aerothermal ablation response of simulated radioisotope power supplies are presented. Full-scale general purpose heat source, graphite impact shell, and lightweight radioisotope heater unit test articles are all tested without nuclear fuel in simulated reentry environments. Convective stagnation heating, stagnation pressure, stagnation surface temperature, surface recession profile, and weight loss measurements are obtained for diffusion-limited and sublimation ablation conditions. The recession profile and weight loss measurements show an effect of surface features on the stagnation face. The surface features alter the local heating which in turn affects the local ablation. NomenclatureA s = surface area, mm 2 D = module diameter, mm H t = total enthalpy, MJ/kg m = mass loss, g P a -stagnation pressure behind the shock, atm #o i = stagnation heat flux for 0.3048-m-radius sphere, W/cm 2 s = module surface recession, mm T w = wall temperature, K t = minimum aeroshell thickness, mm X -vertical position with respect to nozzle center, mm Y = horizontal position with respect to nozzle center, mm p = ablating material density, g/cm 3Subscripts av = average ref = reference t = Total w = wall

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Section: Nomenclaturementioning

confidence: 99%

Ablation response testing of simulated radioisotope power supplies

Lutz

Chan

1994

Journal of Spacecraft and Rockets

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“…and at critical time (Af) C r» is The average thermomechanical-erosion rate is T V ~ ASXP/ (6) Combining Eqs. (1-6) and mass-balanced relation, then yields:…”

Section: Mechanism Of the Particle Erosion For Carbon-base Materials mentioning

confidence: 99%

Theoretical analysis for mechanical erosion of carbon-base materials in ablation

Ren

Sun

Liu

1996

Journal of Thermophysics and Heat Transfer

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This article derives and provides a theoretical analysis for the mechanical erosion of carbon-base materials in ablation. The theory of mechanical erosion based on a nondimensional critical roughness parameter is proposed. The important parameters in this analytical method are independent of the test. The analysis accounts for the heating, pressure, and shear forces acting on material particles exposed to the boundary-layer flow. For the validity of a theoretical analytical method a computational example is given. The theoretical results agree fairly with the experimental data.Nomenclature a = characteristic height of ablated filler particle C f = skin friction coefficient d -particle size h -height of exposed filler particle hs = equivalent sand roughness M = average molecular weight of gas phase at wall m = mass loss rate p = static pressure Q -drag force R -universal gas constant S = surface recession rate T = wall temperature t = time u c = boundary-layer-edge velocity x = surface distance j8 = fraction of particle surface attached to surrounding matrix AS = surface recession p = surface density of heat shield p e = density at boundary-layer edge p w = gas density at wall a = tensile stress cr u = ultimate strength of particle-matrix bound Subscripts b -binder material c = based on thermochemical mass removal rate of " carbon element ch = based on thermochemical ablation theory cr = point of filler particle removal / = filler material m = maximum value me = based on mechanical erosion theory to = total Presented as Paper

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“…This expression was specified by Park [37] based on fits to the results of a range of experiments [38][39][40][41][42][43][44], and varies from around 0.01 at room temperature to 0.3 at 3000 K. Figure 2.1 shows a plot of this fit, labelled as "EQ. (1)", alongside the relevant experimental data.…”

Section: Oxidationmentioning

confidence: 99%

“…Due to the high costs associated with in-flight testing, ground testing stands as a cost-effective method for reducing modeling uncertainties. Ablation testing has often been conducted in long-duration facilities such as arc jets [12,44,46,[68][69][70]. These facilities are capable of providing representative surface heat fluxes and excel at investigating the in-depth response of TPS materials.…”

Section: Introductionmentioning

confidence: 99%

“…Ablation testing is generally conducted in long-duration facilities such as arc jets [12,44,46,[68][69][70], which are suitable for investigating the in-depth material response due to their ability to provide representative heating rates for extended periods. They are, however, unable to reproduce a realistic in-flight shock layer due to low Reynolds numbers and, depending on the facility type, a high degree of thermal and chemical nonequilibrium in the freestream.…”

Section: Introductionmentioning

confidence: 99%

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Hypervelocity shock layer emission spectroscopy with high temperature ablating models

Lewis¹

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During reentry into the atmosphere, a vehicle can encounter extreme convective and possibly radiative heating loads. Such spacecraft must rely on a carefully designed thermal protection system to maintain the integrity of the underlying structure, thus ensuring the survival of any cargo or crew it may contain. Despite many past developments and research efforts, to this day there remain large uncertainties associated with the prediction of heat shield performance. In particular, accurate modelling of ablation phenomena is critical to minimising uncertainties, reducing excess weight, and increasing safety. This includes thermochemical ablation by oxidation, nitridation, and sublimation, as well as the mechanical removal of material via spallation. Due to the high costs associated with in-flight testing, and the difficulty of mounting precision instruments and advanced diagnostics on flight vehicles, ground-based experiments stand as a cost-effective method for reducing modelling uncertainties.Ablation testing is generally conducted in long-duration facilities such as arc jets, which are well suited to investigating in-depth material response due to their ability to provide representative heating rates for extended periods. They are, however, unable to reproduce a realistic in-flight shock layer due to low Reynolds numbers and, depending on the facility type, a high degree of thermal and chemical nonequilibrium in the free-stream. In contrast, impulse facilities such as shock tubes and their variants are well suited to reproducing realistic flight conditions with free-streams that are a closer match for flows dominated by binary processes in terms of Reynolds number, temperature, and chemical composition. Due to their extremely short test times, however, ranging from the order of 10 µs to several milliseconds, they are unable to aerothermally heat test models up to representative in-flight temperatures, or recreate the quasi-steady heat and mass flux balance of flight. This key limitation of impulse facilities was recently overcome in experiments using the University of Queensland's X2 expansion tunnel by electrically pre-heating samples to temperatures approaching 2500 K immediately prior to a test.In this work, the pre-heating methodology was enhanced to generate maximum surface temperatures approaching 3300 K in order to study sublimation phenomena. It was found that although sublimation-regime temperatures could be achieved, the relevant surface processes themselves were suppressed due to the high pitot pressures of the conditions used. Instead, the nitridation process was studied by observing air shock layer CN emissions with pure graphite models heated to surface temperatures ranging from 1770-3300 K. These results were compared with numerical simulations which predicted a monotonic increase of emissions with surface temperature for all models considered, whereas the experiments showed an initial increase from 1770-2500 K and then remained relatively constant from 2500-3300 K. The simulations also su...

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Ablation of ATJ Graphite at High Temperatures

Cited by 56 publications

References 9 publications

Ablation response testing of simulated radioisotope power supplies

Ablation response testing of simulated radioisotope power supplies

Theoretical analysis for mechanical erosion of carbon-base materials in ablation

Hypervelocity shock layer emission spectroscopy with high temperature ablating models

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